Many eukaryotic cells are enveloped by an extracellular matrix of proteins that provide structural support, cell and tissue identity, and autocrine, paracrine and juxtacrine properties for the cell within its environment (McGowan, S. E. (1992) FASEB J. 6: 2895-2904). The diverse biochemistry of extracellular matrix proteins (ECMP) is indicative of the many, often overlapping, roles that are attributed to each distinct molecule (cf. Grant, D. S. and Kleinman, H. K. (1997) EXS 79: 317-333). Whilst a great number of ECMPs have been isolated, it still remains unclear how the majority interact with other ECMPs or with molecules residing within the cell membrane. Many ECMPs have been associated with tissue growth and cell proliferation, others with tissue or cell differentiation, and yet others with cell death (cf. Taipale, J. and Keski-Oja, J. (1997) FASEB J. 11: 51-59; Eleftheriou, C. S. et al. (1991) Mutat. Res. 256: 127-138).
Multidomain or mosaic proteins play an important role in the diverse functions of the extracellular matrix (ECM) in various tissues (Engel, J. et al. (1994) Development (Camb.) (suppl.) 35-42). Cartilage matrix protein (CMP) is an abundant structural component of the ECM in some types of hyaline cartilage. It binds to aggrecan, the large cartilage proteoglycan, and to cartilage collagen fibrils; and it may serve to connect the two major macromolecular networks (Deak, F. et al. (1997) J. Biol. Chem. 272: 9268-9274).
The primary structure of the CMP monomer has been determined from the nucleotide sequences of human and mouse (Jenkins, R. N. et al. (1990) J. Biol. Chem. 265: 19624-19631; Aszodi, A. et al. (1996) Eur. J. Biochem. 236: 970-977). After cleavage of the signal peptide, each monomer of CMP consists of two von Willebrand factor type A (vWFA)-like modules (collagen-binding motifs) separated by an epidermal growth factor (EGF)-like module and followed by a C-terminal domain. CMP transcript is evenly distributed in the developing mouse skeleton and in late gestation follows a zonal distribution paralleling hypertrophy and calcification; extraskeletal expression of CMP mRNA is detected in the eye [Aszodi, A. et al. (supra)].
CMP is one of the simplest members of the vWFA-like module superfamily, a diverse group of proteins sharing high sequence similarity over a segment. The vWFA-like module was first identified as the repeated type A domain of von Willebrand factor and has since been found not only in plasma proteins but also in plasma membrane and ECM proteins (Colombatti, A. and Bonaldo, P. (1991) Blood 77: 2305-2315). Crystal structure analysis of an integrin vWFA-like module has revealed a classic/"Rossmann" fold and suggested a metal ion-dependent adhesion site. This adhesion site is conserved in other vWFA-like modules and can be involved in binding protein ligands (Lee, J.-O. et al. (1995) Cell 80: 631-638).
A second CMP-like protein, matrilin-2, which shares many characteristics of CMP has recently been identified [Deak, et al. (supra)]. Murine matrilin-2 consists of one vWFA-like domain, ten epidermal growth factor (EGF)-like modules and a C-terminal domain which contains a coiled-coil motif. In addition, matrilin-2 has a N-terminal region rich in positively charged amino acid residues. Conserved homologies between the two proteins, CMP and matrilin-2, suggested that CMP be renamed as matrilin-1 [Deak, et al. (supra)]. Murine matrilin-2 differs from matrilin-1 in that it is detected in diverse tissue types. It is most abundant in embryonic limbs; in calvaria, uterus, heart and brain from newborn mice; and in murine fibroblast and rat osteoblast cell lines [Deak, et al. (supra)].
Elevated serum or synovial fluid levels of cartilage-specific markers, such as the cartilage oligomeric matrix protein (COMP) in patients with rheumatoid arthritis and in animal models of osteoarthritis, may be used to predict disease progression (Saxne, T. and Heinegard, D. (1992) Br. J. Rheumatol 31: 583-591; Malemud, C. J. (1993) Curr. Opin. Rheumatol. 5: 494-502). Chondrodysplasias are characterized by abnormal development of articulating joints and bone. Two loci have been linked within several chondrodysplasia pedigrees. Collagen type II, collagen type X, and CMP have been excluded as disease loci, and mutations in COMP have been linked to pseudochondrodysplasia (Loughlin, J. et al. (1994) Hum. Genet. 94: 698-700; Hecht, J. T. et al. (1995) Nat. Genet. 10: 325-329).
The discovery of a new human matrilin-3 and the polynucleotides encoding it satisfies a need in the art by providing new compositions which are useful in the diagnosis, prevention and treatment of developmental, vesicle trafficking, neoplastic, and immunological disorders.